The present invention relates to one part heat curable organopolysiloxane compositions having improved shelf stability. More particularly, the present invention relates to the employment of certain azo inhibitors in a platinum group metal catalyzed one part heat curable organopolysiloxane composition.
Prior to the present invention, as shown by Eckberg, U.S. Pat. No. 4, 670,531 and Cavezzan et al, U.S. Pat. No. 4,640,939, azodicarboxylates, such as dialkylazodicarboxylates were used to inhibit reaction between an organopolysiloxane base polymer having olefinically unsaturated organic radicals and an organohydrogenpolysiloxane which were catalyzed by an effective amount of a precious metal containing catalyst, such as platinum. Although valuable results can be achieved by the use of such dialkylazodicarboxylate inhibitors, experience has shown that the shelf life of the resulting heat curable organopolysiloxane compositions is often insufficient to satisfy the requirements for many heat curable organopolysiloxane composition applications. Accordingly, additional inhibitors are constantly being sought by the silicone industry to extend the shelf life of one part heat curable organopolysiloxane compositions.